1. Field of the Invention
The present invention relates to a driving mechanism for driving a gear pump of a dual drive type for imparting pressure to a molten, highly viscous resin and, more particularly, to a driving mechanism facilitating the alignment of a coupling for coupling the driving mechanism and a gear pump of a two-shaft drive type for pumping a molten, highly viscous resin.
2. Description of the Prior Art
FIGS. 5 to 9 show a known driving mechanism for driving a gear pump of a two-shaft drive type for imparting pressure to a molten, highly viscous resin. The general construction of a kneading/pelletizing machine provided with a gear pump for imparting pressure to the material will be described with reference to FIG. 9 prior to the description of a driving mechanism. The kneading/pelletizing machine comprises a kneader 31, a gear pump 32 and a pelletizer 33. A material containing a resin and additives is supplied continuously at a fixed rate from a hopper 34 into the chamber 35 of the kneader 31. The material is kneaded in the chamber 35 with two parallel rotors 36 extended within the chamber 35 while the same is heated for melting. Then, the molten material is fed by pressure to the pelletizer 33 by a gear pump 32 connected to the discharge port 37 of the kneader 31. The pelletizer 33 extrudes the molten material fed by pressure thereto by the gear pump 32 through a die, and cuts the extruded material with a rotary knife rotating at a high rotating speed to produce pellets continuously.
Referring to FIGS. 5 and 6, the gear pump 32 comprises a pump case 43 having an inlet port 41 connected to the kneader 31 and an outlet port 42 connected to the pelletizer 33, and a pair of gear rotors 48 and 49 integrally having gear wheels 44 and 45 and shafts 46 and 47, respectively, and disposed with the axes of the shafts 46 and 47 in parallel to each other within the pump case 43. The pair of gear rotors 48 and 49 are rotated respectively in opposite directions to suck the molten material through the inlet port 41. The molten material is confined in spaces B defined by the teeth of the gear wheels 44 and 45 and the inner surface of the pump case 43, conveyed toward the outlet port 42 as the gear wheels 44 and 45 rotate and delivered at a high pressure through the outlet port 42 into the pelletizer 33. When the molten material has a relatively low viscosity, only one of the gear wheels 44 and 45 may be driven by a driving mechanism and the other gear wheel engaging the gear wheel driven by the driving mechanism is driven by the former gear wheel. When the molten material has a relatively high viscosity, the tooth faces of the engaged gear wheels 44 and 45 are abraded rapidly due to the insufficient lubricating performance of the molten material and the abrasive action of the additives, if only one of the gear wheels 44 and 45 is driven positively. Accordingly, a gear pump of a dual drive type having a pair of gear wheels which are not engaged and driven individually is employed in pumping such a molten material having a relatively high viscosity.
Referring to FIG. 5, a driving mechanism for driving both the shafts 46 and 47 of the gear pump 32, the driving mechanism comprises a motor 55, a reduction gear 56 for reducing the output speed of the motor 55 and increasing the output torque of the motor 55, and a reversing gear 57 having two output shafts 58 and 59 that rotate synchronously in opposite directions, respectively, at the same rotating speed. The shafts 46 and 47 of the gear pump 32 are connected to the output shafts 58 and 59 of the reversing gear 57 with a pair of gear couplings 61 and 62 each having coupling heads 60 at the opposite ends thereof, respectively. As shown in FIG. 7, each coupling head 60 has two sets of coupling units each comprising a coupling case 63 provided with an internal spur gear 63a, and a coupling block 64 provided with a crowned, external spur gear 64a engaging the internal spur gear 63a of the coupling case 63. The internal spur gears 63a and the external spur gears 64a are engaged properly even if the output shafts 58 and 59 of the reversing gear 57 are not aligned precisely with the shafts 46 and 47 of the gear pump 32, so that the driving force of the driving mechanism can be smoothly transmitted to the gear pump 32.
When connecting the gear pump to the driving mechanism, the upper coupling 61 and the lower gear coupling 62 are disposed between the output shafts 58 of the reversing gear 57 and the shaft 46 of the gear pump 32 and between the output shaft 59 of the reversing gear 57 and the shaft 47 of the gear pump 32, respectively, and both the coupling heads 60 of the lower gear coupling 62, and the coupling head 60 of the upper gear coupling 61 on the side of the reversing gear 57 are assembled. Then, the respective angular positions of the gear wheels 44 and 45 of the gear pump 32 are adjusted so that the backlash is divided equally for the opposite sides of each tooth of the gear wheels 44 and 45, that is, the angular positions of the gear wheels 44 and 45 are adjusted so that each tooth of one of the gear wheels 44 and 45 is positioned at the middle of the tooth space between the adjacent teeth of the other gear wheel and the teeth of the gear wheels 44 and 45 are not engaged. Then, the coupling head 60 of the upper gear coupling 61 on the side of the gear pump 32 is assembled. In this state, the respective phases of the two external spur gears 64a of the coupling head 60 of the upper gear coupling 61 on the side of the gear pump 32 are not equal to each other. Therefore, the shaft 65 of the upper gear coupling 61 is divided into two portions 65a and 65b, and the two portions 65a and 65b are connected together with a flange coupling 66 so that both the external spur gears 64a of the coupling head 60 engage the corresponding internal spur gears 63a, and then the relative position of the components of the flange coupling 66 is fixed with locating pins 67.
When connecting the gear pump 32 to the reversing gear 57, the flange coupling 66 must be adjusted by delicate gaging requiring skill to compensate the difference between the respective phases of the external spur gears 64a of the coupling head 60 of the upper gear coupling 61 on the side of the gear pump 32. The kneading/pelletizing machine of this kind is subjected to overhaul once a year for the replacement of abraded parts including the gears, and the foregoing delicate gaging of the flange coupling 66 is required every time the kneading/pelletizing machine is overhauled.